1. Field of the Invention
The invention relates to subsea wellhead assemblies; and, more particularly, to apparatus and method for orienting a pair of drill strings within a blowout preventer which drill string extends from a vessel floating on the surface of a body of water down into a subsea wellhead assembly.
2. Description of the Prior Art
In the oil well industry, certain assemblies have been used for drilling oil wells in subsea locations. Generally, such assemblies include a riser carrying a string of drill pipe used to carry out the drilling operations. The string of pipe extends through a conventional B.O.P. stack down into the well borehole.
In certain subsea operations, it may be desirable to have more than one string of oil well drilling or production pipe extending through the riser and through one or more blowout preventers down into the subsea wellhead. If a single drill string is used, when the blowout preventer is actuated, it seals around the single drill string. However, when dual drill strings are provided, in order to obtain a proper and effective seal of the blowout preventer about the dual drill strings, it is necessary that they be initially moved to a central position within the bore extending through the blowout preventer. If they are not in this position when the blowout preventer (or preventers) is actuated, the dual drill strings may not be completely sealed off from the subsea well which might result in considerable damage to equipment or the like as the pressures build up during drilling operations. Heretofore, no satisfactory means have been found for properly orienting dual drill strings in the bore through a blowout preventer without deforming or crushing the drill strings.